Make \retval commands non-empty

Pacify Clang >=15 which complained:
```
include/psa/crypto.h:91:23: error: empty paragraph passed to '\retval' command [-Werror,-Wdocumentation]
 * \retval #PSA_SUCCESS
   ~~~~~~~~~~~~~~~~~~~^
```

This commit performs the following systematic replacement:
```
perl -i -0777 -p -e 's/([\\@])(retval +\S+)\n(?! *\*? *([^\n \\*\/]|\\[cp]\b))/$1$2 ${1}emptydescription\n/g' $(git ls-files '*.[hc]' '*.function' '*.jinja')
```
i.e. add an `\emptydescription` argument to `\retval` commands (or
`@retval`, which we don't normally used) that are followed by a single word,
unless the next line looks like it contains text which would be the
description.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/psa_crypto_hash.h b/library/psa_crypto_hash.h
index ab07231..1c1b451 100644
--- a/library/psa_crypto_hash.h
+++ b/library/psa_crypto_hash.h
@@ -57,8 +57,8 @@
  *         \p alg is not supported
  * \retval #PSA_ERROR_BUFFER_TOO_SMALL
  *         \p hash_size is too small
- * \retval #PSA_ERROR_INSUFFICIENT_MEMORY
- * \retval #PSA_ERROR_CORRUPTION_DETECTED
+ * \retval #PSA_ERROR_INSUFFICIENT_MEMORY \emptydescription
+ * \retval #PSA_ERROR_CORRUPTION_DETECTED \emptydescription
  */
 psa_status_t mbedtls_psa_hash_compute(
     psa_algorithm_t alg,
@@ -97,8 +97,8 @@
  *         \p alg is not supported
  * \retval #PSA_ERROR_BAD_STATE
  *         The operation state is not valid (it must be inactive).
- * \retval #PSA_ERROR_INSUFFICIENT_MEMORY
- * \retval #PSA_ERROR_CORRUPTION_DETECTED
+ * \retval #PSA_ERROR_INSUFFICIENT_MEMORY \emptydescription
+ * \retval #PSA_ERROR_CORRUPTION_DETECTED \emptydescription
  */
 psa_status_t mbedtls_psa_hash_setup(
     mbedtls_psa_hash_operation_t *operation,
@@ -124,13 +124,13 @@
  * \param[in,out] target_operation  The operation object to set up.
  *                                  It must be initialized but not active.
  *
- * \retval #PSA_SUCCESS
+ * \retval #PSA_SUCCESS \emptydescription
  * \retval #PSA_ERROR_BAD_STATE
  *         The \p source_operation state is not valid (it must be active).
  * \retval #PSA_ERROR_BAD_STATE
  *         The \p target_operation state is not valid (it must be inactive).
- * \retval #PSA_ERROR_CORRUPTION_DETECTED
- * \retval #PSA_ERROR_INSUFFICIENT_MEMORY
+ * \retval #PSA_ERROR_CORRUPTION_DETECTED \emptydescription
+ * \retval #PSA_ERROR_INSUFFICIENT_MEMORY \emptydescription
  */
 psa_status_t mbedtls_psa_hash_clone(
     const mbedtls_psa_hash_operation_t *source_operation,
@@ -156,8 +156,8 @@
  *         Success.
  * \retval #PSA_ERROR_BAD_STATE
  *         The operation state is not valid (it must be active).
- * \retval #PSA_ERROR_INSUFFICIENT_MEMORY
- * \retval #PSA_ERROR_CORRUPTION_DETECTED
+ * \retval #PSA_ERROR_INSUFFICIENT_MEMORY \emptydescription
+ * \retval #PSA_ERROR_CORRUPTION_DETECTED \emptydescription
  */
 psa_status_t mbedtls_psa_hash_update(
     mbedtls_psa_hash_operation_t *operation,
@@ -195,8 +195,8 @@
  *         The size of the \p hash buffer is too small. You can determine a
  *         sufficient buffer size by calling #PSA_HASH_LENGTH(\c alg)
  *         where \c alg is the hash algorithm that is calculated.
- * \retval #PSA_ERROR_INSUFFICIENT_MEMORY
- * \retval #PSA_ERROR_CORRUPTION_DETECTED
+ * \retval #PSA_ERROR_INSUFFICIENT_MEMORY \emptydescription
+ * \retval #PSA_ERROR_CORRUPTION_DETECTED \emptydescription
  */
 psa_status_t mbedtls_psa_hash_finish(
     mbedtls_psa_hash_operation_t *operation,
@@ -225,8 +225,8 @@
  *
  * \param[in,out] operation     Initialized hash operation.
  *
- * \retval #PSA_SUCCESS
- * \retval #PSA_ERROR_CORRUPTION_DETECTED
+ * \retval #PSA_SUCCESS \emptydescription
+ * \retval #PSA_ERROR_CORRUPTION_DETECTED \emptydescription
  */
 psa_status_t mbedtls_psa_hash_abort(
     mbedtls_psa_hash_operation_t *operation);